Insensitive, non-toxic and inexpensive explosives, mostly based on ammonium nitrate, are preferentially used in civil blasting applications. In salt mining or tunnel driving, for example, so-called pumping explosives are used in addition to the long familiar ANFO. Pump explosives are differentiated into emulsion explosives and suspension explosives (slurries, explosive slurries).
ANFO (Ammonium Nitrate Fuel, trade name e.g. ANDEX) is a mixture of porous ammonium nitrate and mineral oil or diesel oil (fuel oil), which is used in the mining industry as a safe-to-handle explosive.
In addition, if not sufficient for safe ignition, these explosives require so-called primary explosives in conjunction with detonator-sensitive assembled initiation charges (boosters, amplifier charges or primers). Primary explosives can be found in commercial detonators. Primary explosives are characterized by high sensitivity to friction, shock, impact and heat. Mercury fulminate, for example, can already be detonated by heating to 160° C. (detonating cord) or by a 2 kg drop hammer falling from a height of 4 cm. Initial detonation with blasting caps was invented in 1862 by Alfred Nobel. Important primary explosives are mercury fulminate, lead azide, silver azide, silver acetylide, silver fulminate, diazodinitrophenol, lead picrate (trinitrophenol lead), lead styphnate (lead trinitroresorcinate), tetracene, nickel hydrazine nitrate (NHN), hexamethylene triperoxide diamine (HMTD), acetone peroxide (DADP, TATP or APEX), 3-nitrobenzenediazonium perchlorate, mercury azides, tetraamine copper (II) chlorate (TACC) and copper acetylide.
Pressed cylindrical explosive devices made of tetryl, trinitrotoluene, phlegmatized (reduction of sensitivity) hexogen, pentaerythritol tetranitrate (PETN), picric acid and other explosives are usually used as detonator-sensitive assembled booster charges, also referred to as initial gain detonator or IG detonator. Common to all these substances is a greater sensitivity to the initial pulse than that of the explosive of the main charge (e.g. ANFO, cast TNT, powdery explosives). Primer cartridges of gelatinized explosives are often used in rock blasting as an additional amplification charge to initiate the main charge of powdery explosives or emulsion explosives. The weight and the shape of the IG detonator are calculated so that, at detonation, a pulse is produced that ensures the triggering of the detonation of the main charge and the desired detonation behavior. The initiation of the IG detonator is triggered by a blasting cap, an electric detonator or a NE-igniter (non-electric igniter).
The problem with the IG detonators used to date is that they either consist of long term no longer available military explosives (pressed TNT, cast Composition B, etc.), or that classic primer cartridges made of gelatinous explosives (dynamite successors on the basis of blasting oil) are used, which becomes problematic in the long term. Besides the increased health hazard from nitric acid ester, the complicated and hazardous production and the associated high cost are a significant issue.
U.S. Pat. No. 3,902,933 A discloses an initial explosive charge for detonation of nitromethane. The initial explosive charge is formed by a polyurethane foam containing dispersed microspheres. The microspheres can be hollow glass microspheres, resin beads, ceramic beads, etc.
Further disclosed, in U.S. Pat. No. 4,334,476 A, is an initial explosive charge for granular or liquid explosives, with an interior channel to hold the ignition device, whereby the interior channel exhibits a small wall thickness so as to improve the detonation. This ensures the separation of the liquid explosive and the ignition device.
Finally, U.S. Pat. No. 3,797,392 A discloses microspheres, used for the sensitization of liquid explosives. These microspheres, such as hollow glass spheres, ceramic microspheres or silicon carbide, are dispersed in the liquid explosive right away and subsequently ignited. The use of open-pored polyurethane foams is described as well.